A transistor is widely utilized as an important semiconductor electronic device for constituting a display and computer equipment, and is currently produced using an inorganic material such as polysilicon and amorphous silicon for a semiconductor material. In production of a thin film transistor in which such an inorganic material is used, a vacuum process and a high-temperature process are required, and a problem is that a production cost is high. In addition, a high-temperature process is included to thereby limit a usable substrate, and, for example, a glass substrate is mainly used. The glass substrate, however, is high in heat resistance, but is poor in impact resistance, difficult to be lighter, poor in flexibility, and thus difficult to form a flexible transistor.
In recent years, an organic electronic device in which an organic semiconductor material is used has been actively researched and developed. The organic semiconductor material can easily form a thin film by a simple method by means of a wet process such as a printing method or a spin coat method, and has an advantage of allowing a production process temperature to be lowered, as compared with the case of a conventional transistor in which the inorganic semiconductor material is utilized. Thus, the thin film can be formed on a plastic substrate generally low in heat resistance, reductions in weight and cost of an electronics device such as a display can be realized, and various evolvements such as an application in which the flexibility of the plastic substrate is utilized can be expected.
It is known that a low-molecular semiconductor material such as pentacene is used as the organic semiconductor material to thereby exhibit a high semiconductor device performance. An unsubstituted acene type compound typified by pentacene, however, is often poor in solubility in a solvent due to strong intermolecular interaction by a n-conjugated system. Therefore, a composition for organic transistor production including such a compound in a high concentration cannot be prepared, and an organic semiconductor formed by a printing method has a small crystal grain and has the problems of being energized only by application of a high voltage, of peeling of an insulating film by application of a high voltage, or the like.
As a method for solving the above problems, Non Patent Literature 1 discloses use of a compound that is an acene type compound having a substituent for imparting solubility, as an organic semiconductor material. The acene type compound having a substituent, however, often has the problem of being low in charge mobility as compared with the unsubstituted acene type compound.
In addition, Patent Literatures 1 and 2 disclose that a solvent such as an aryl halide, typified by 1,2,4-trichlorobenzene, or tetralin excellent in solubility of an organic semiconductor material is used for dissolution with heating. A hardly-soluble organic semiconductor material, however, is required to be dissolved by dissolution with heating at high temperatures, and a problem is that the organic semiconductor material is precipitated by cooling in the subsequent coating process. Furthermore, the aryl halide has concerns about ecological toxicity, and is also problematic in terms of work safety.